Discovering service-on-demand for large numbers of functionality-similar web services is one of the key issues in services discovery study. According to the functionality-similar web services, a service-on-demand discovery process is proposed in this paper. To meet the target, FCM clustering is adopted for agglomerative clustering between the user's QoS demand information and the QoS information of Web Service resource. Then, the sequence could be determined by similarity computation in the same classification clustering. Lastly, the numerical example is presented to illustrate that the service-on-demand can be discovered efficiently to optimize network resources and improve the efficiency.